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The STX 100: History and Specs

Updated: Oct 8, 2019

Before we had the Spectra 1964 STX 100 500 series preamp, we had the Spectra Sonics Model 110A, and before that, we had the Spectra Sonics Model 101 Preamplifier. Introduced in 1965, the Model 101 Preamplifier was the standard by which all other solid state audio amplifiers were judged. The performance and reliability of the 101 established a standard never seen before in the recording industry. Its total harmonic distortion (thd) and intermodulation distortion (imd) measurements were below the residual level of the test equipment of the day, and its noise figure below -127dBu, unweighted. In addition, the 101 was the first solid state audio amplifier to provide peak overload capability of up to 1000%. The 101 Preamplifier was utilized in early Spectra Sonics recording console design, as well as installed in many consoles built by separate manufacturers. The early sounds of Stax and Ardent Studios in Memphis, as well as Muscle Shoals Sound Studio in Alabama is attributed greatly to the Model 101 Preamplifier.

The Model 101 is unchanged today, and is available alone, or incorporated into many of our products, like the Model 610 Complimiter and the M-502 Pro. The maximum output of the 101 is +18dBu.

Used in late Spectra Sonics console designs, the 110A Preamplifier Module had improved headroom and noise specifications, and a very "clean" reputation.
110 A Preamplifier Module, the updated version of the Model 101

Next, came the model 110A Preamplifier. It's an updated version of the Model 101, which implements a bi-polar design (+/- 24V Volt). It was introduced in 1971, and was used in late Spectra Sonics console design. It's improved headroom and noise specifications earned it an even more "clean" reputation than the original 101 preamp. Its increased maximum output of +24dBu makes it extremely versatile, especially in modern digital recording studios.

Today, we have the STX 100. It's is a 500 Series version of the classic Spectra Sonics 101 amplifier circuit. The STX 100 is a high-bandwidth microphone preamplifier with 64dB of gain and a 10Hz to 50KHz frequency response. A 10dB input pad and a dual potentiometer offers continuously variable input pad and output level controls allow the STX 100 to be used with both microphone and line level sources.

The Spectra 1964 STX 100. Famous Spectra Sonics technology made affordable.

The STX 100 represents an affordable alternative for employing the same Spectra Sonics technology of our famous recording desks made over 40 years ago. The unique circuit topology of the STX 100 utilizes a 100 series discrete preamplifier design that was at the heart of every console built by the company. The result is unequaled performance in terms of expanded dynamic range (headroom), low noise and distortion, as well as extended harmonic content of the amplified signal.

Most, if not all, conventional analog audio amplifiers live in a world whereby dynamic range limitations are dictated by audio program peaks. Audio program peaks, which can average 6dB to over 20dB, effectively reduce the undistorted output of a given amplifier by that peak to average ratio. The reduction in output limits headroom (dynamic range), increases numerous forms of distortion, and limits the harmonic content of the amplified audio signal.

The STX series lives in the VU world, irrespective of peak to average transient audio program signal material. When a percussion instrument is the source, it is not uncommon to measure transient peaks that are 12dB-24dB above the program material average. Again, the STX series products are not affected by the high transient peak excursions. The first and second stages of the STX 100 utilize independent LED overload indicators to monitor program overload conditions. The result is faster set-up time with consistent and definable results. Drums sound like you are positioned next to them. Guitars have full harmonic content. The dynamic range of vocals is preserved.


Gain: 64dB

THD: Less than .01% @ 20Hz-20KHz

Signal/Noise: Better than 120dB, (unweighted)

Maximum Output: +18dBm, 20Hz–20KHz

Power Requirement: Less than 50mA, +18dBm

Input/Output Control: Continuously Variable/10dB Pad

Input Impedance: 5K Ohms, Nominal

Output Impedance: Less than 50 Ohms

Frequency Response: 10Hz-50KHz

Phantom: 48 Volts

Polarity: 180 Degrees/Reverse/Mic or Line Input


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